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Pregnancy Hormones

Dr. Milroy J Samuel

Reviewed by
Dr. Milroy J Samuel

Certain hormones in our bodies are essential for sex drive, reproduction, menstrual cycles, and ovulation. In this article we will cover what each one does and then explain how they make one another work.

GnRH

GnRH is necessary for correct reproductive function. It is produced by a small gland deep in the brain called the hypothalamus, which controls ovulation and corpus luteum maintenance in women and spermatogenesis in men. GnRH stands for Gonadotropin Releasing Hormone. The gonadotropins are the reproductive hormones FSH (Follicle Stimulating Hormone) and LH (Luteinizing Hormone), which are produced by another gland in the brain called the pituitary gland.

GnRH is considered a neurohormone, and it controls and stimulates the secretion of the hormones FSH and LH. Infrequent pulses of GnRH lead to FSH release, and more frequent pulses lead to LH release. The difference between men and women is that these pulses keep a consistent rhythm in men, whereas in women the pulses vary during the menstrual cycle and a very large amount of GnRH is secreted right before ovulation.

FSH

FSH stands for Follicle Stimulating Hormone, which is essential in the reproduction process for both men and women. This hormone stimulates the maturation of ovarian follicles in women, and it is critical for sperm production in men. FSH is secreted from cells in the anterior pituitary gland and acts synergistically with LH (Luteinizing Hormone) in reproduction. These hormones are at their lowest levels late in the follicular phase, and at the end of the luteal phase there is a slight increase, which is necessary to begin the next ovulatory cycle.

FSH: The Boss

FSH levels can determine things like fertility. FSH regulates the development, growth, pubertal maturation, and reproductive processes of the human body. FSH also stimulates the development of the Graafian follicle, which is a small egg inside the ovary.

Men and Women

In women, FSH affects the menstrual cycle and the production of eggs. The amount of FSH varies throughout the menstrual cycle, but is always at its peak just before the woman releases an egg (ovulates). In men FSH controls the production of sperm, and the level of FSH tends to stay constant in men, with little or no variance.

Luteinizing Hormone (LH)

Luteinizing Hormone, also known as LH, is also produced by the anterior pituitary gland. This hormone is found in both men and women, and is essential for reproduction in both sexes. In women, a large rise of LH (known as an LH surge) triggers ovulation. Testing for this is the basis of most urine ovulation predictor kits, as ovulation in females tends to occur 12–36 hours after the LH surge. In men, LH stimulates the Leydig cell, which produces testosterone, but LH has nothing to do with actual sperm production.

Levels

Regardless of your gender, LH levels are very low during childhood and gradually rise as your body begins to mature. In men, low levels of LH can cause low sperm counts due to low testosterone production. In women, low LH levels can result in a missed menstrual period due to failure to ovulate. High levels occur during an LH surge, and after menopause women experience high levels at all times (the body makes more in an attempt to get the ovary to respond, which no longer occurs after menopause).

LH is required for the continued development and function of the corpus luteum, which is where its name comes from. LH luteinizes the follicle right after ovulation, converting the now empty follicle from an egg-releasing structure to a progesterone hormone-producing gland. The progesterone phase is also called the luteal phase of the menstrual cycle, and it lasts about 12–14 days. If a woman is experiencing a low level of LH during her reproductive years, she can now be treated with human LH (Luveris).

An LH surge is a sudden increase in the amount of LH released, which causes the egg to leave the ovary (ovulation) and make its way toward the uterus. These surges don’t last very long — usually 24 to 36 hours — as the amount increases dramatically just before the most fertile day of a woman’s cycle.

Ovulation Predictor Tests

Urine ovulation prediction kits (OPKs) are designed to detect this LH surge. When the result turns from negative one day to positive the next day, ovulation is likely to occur within the next 12–36 hours.

OPK tests can be bought over the counter at a reasonable price, but understand that certain prescription drugs can affect the results. If you’re testing for your LH surge, many people will tell you to test in the morning hours, since this is the time of day other fertility tests are done. But you will probably obtain better results if you test in the evening hours, when there is more LH in your urine.

Estrogen

Estrogen is commonly mistaken for an exclusively female hormone, when in fact it is found in men too. Estrogen is responsible for the growth and development of female sexual characteristics and reproduction. Produced in the ovaries, adrenal glands, and fat tissues, estrogen travels through the bloodstream and binds to estrogen receptors on cells in targeted tissues, affecting the breasts, uterus, brain, bone, liver, heart, and other organs.

Estrogen is produced in large amounts right before ovulation, and it helps the uterus to rebuild its lining after menstruation. It also acts as a “feedback” control on the brain hormones LH and FSH. In other words, the two sex hormones estrogen and progesterone travel up to the brain to either increase or decrease the amount of LH and FSH being produced. This feedback helps to regulate the timing of the events of the menstrual cycle.

Types of Estrogen

There are three types of estrogen— Estradiol, Estrone, and Estriol—that control the growth of the uterine lining during the first part of a woman’s menstrual cycle, cause changes in the breasts during adolescence and pregnancy, and regulate processes such as bone growth and cholesterol levels. Here is a brief description of each:

  • Estrone (E1) is produced mainly in the fat cells (adipose cells) of post-menopausal women.
  • Estradiol (E2) is produced mainly in the ovaries of premenopausal women. This is the major biological active form of estrogen in the body.
  • Estriol (E3) is produced by the placenta during pregnancy.

Progesterone

Progesterone thickens the nutrient-based endometrium in preparation to receive a fertilized egg, and also causes a woman’s temperature to rise if conception has taken place.

A woman’s ovaries produce this hormone during the luteal phase, the last two weeks of her monthly cycle after ovulation. Progesterone has many effects on the body, especially during pregnancy. This hormone thickens the uterine lining (endometrium) in preparation to receive a fertilized egg. It also helps the breasts prepare for milk production. The main function of this hormone in the non-pregnant state is to cause the endometrium to secrete proteins during the second half of the menstrual cycle, preparing it for the implantation of a fertilized egg.

Progesterone levels rise during the second half of the menstrual cycle following ovulation. During ovulation, the growing follicle ruptures, releasing the egg. The ovarian tissue that replaces the ruptured follicle becomes a temporary organ called the corpus luteum, which continues to produce estrogen and starts to produce progesterone. The corpus luteum lives for maybe twelve days, after which, if there is no pregnancy, it atrophies and the progesterone it has made disappears. The loss of progesterone initiates the menstrual blood flow.

Progesterone changes the cervical mucus. During ovulation, which is a high estrogen state, cervical mucus tends to be abundant, clear, stretchy, and watery. This type of mucus helps sperm to swim through the cervix on their way to egg fertilization. About two days after ovulation, progesterone production causes the mucus to become thick and cloudy, blocking the sperm’s pathway through the cervix. This same thick mucus persists throughout pregnancy, protecting the uterine cavity from bacteria that naturally live in the vagina. This is the so-called “mucus plug” of pregnancy.

Progesterone is believed to be the cause of PMS, or premenstrual syndrome, which in turn causes breast tenderness, mood swings and that bloated feeling. Some clinics specializing in the treatment of PMS used to use high doses of progesterone (often given rectally!) starting a few days or a week before the period. Unfortunately, this has never been proven to work, and in some cases it can delay the onset of the period and create a false impression of pregnancy (late period, nausea, bloating, and cramping are all early symptoms of pregnancy).

Progesterone raises the body temperature about 0.5 degrees Fahrenheit. This is the basis for the basal body temperature approach to fertility timing. If a woman attempting to become pregnant takes her temperature every morning the moment she wakes up, this number represents the basal temperature of the body (before natural metabolism warms it up). About two days after ovulation, this number goes up about ½ degree. About twelve days later, if there is no pregnancy, the temperature drops and the menstrual period starts in a day or so. If the temperature remains elevated longer than about fourteen days, this is another early way to diagnose a pregnancy. This method can be used to look into the past and estimate when ovulation may have taken place, but it cannot be used to try to predict impending ovulation. For that, the ovulation predictor kit (OPK) is quite effective.

Topical progesterone skin cream is sold as an over-the-counter PMS or menstrual “remedy.” It is the only hormone that can be purchased without a prescription. Other hormones (testosterone, estrogen, insulin, thyroid hormone, and others) require a prescription from a physician. Why is this? Because in the dosages used, this topical cream does almost nothing. Unlike other hormones applied to the skin, progesterone does not cross the skin to any appreciable degree, and when applied topically it does not raise the blood level unless large amounts are used (about 50 times more cream than the jar suggests). Unfortunately, this does not prevent thousands of hormone “clinics” and web sites from heavily promoting and selling this product to poorly informed consumers.

When pregnancy occurs, the first hormone detectable is hCG (human chorionic gonadotropin), sometimes called beta hCG. The major early function of this hormone is to keep the corpus luteum alive and functioning so it continues to produce serum progesterone until the placenta can take over, which happens at about 8–9 weeks of pregnancy.

Progesterone and Pregnancy

Progesterone is produced in the ovaries (by the corpus luteum), the placenta (when a woman gets pregnant) and the adrenal glands (in minimal amounts). Progesterone helps prepare your body for conception and pregnancy, and it regulates a woman’s monthly menstrual cycle. As mentioned, after pregnancy occurs, progesterone is produced in the placenta, and levels remain elevated throughout the pregnancy. The combination of high estrogen and progesterone levels prevents further ovulation during pregnancy, which is why superfecundation in humans is so extremely rare (but not so rare in other mammals).

During the early stages of pregnancy, progesterone levels double and triple compared to what they were before pregnancy. By the end of the first trimester, the placenta fully takes over progesterone production. Some fertility clinics and OB doctors support the first trimester with supplemental progesterone in select patients. This is normally stopped at about twelve weeks, since the body’s natural placenta production should be more than enough by week 9 or 10.

Elevated progesterone levels during pregnancy are also crucial for the survival of the fetus, as the increase in progesterone helps keep the uterus from contracting and promotes the growth of blood vessels, giving your baby the nourishment it needs. Progesterone levels rise to fifteen times normal by the third trimester.

Another function of progesterone is the relaxation of skeletal ligaments. This is one reason why pregnant women have so much low back, hip, and pelvic pain during pregnancy. This relaxation helps the birth canal to expand and stretch a little to help the baby fit through during labor.

For the past few years, progesterone has been used to help prevent premature birth in high-risk pregnancies. If a pregnant woman has given birth prematurely (prior to 37 weeks) with a previous pregnancy, she might be a candidate for a weekly injection of a long-acting synthetic progesterone, given from about week 16 to week 36. If during pregnancy an otherwise low risk patient is identified as having a shortening of her cervix, she might be a candidate for nightly vaginal progesterone (100 percent bio-identical), starting when the diagnosis is made and continuing to 36 weeks.

After delivery of a baby and removal of the placenta, progesterone levels drop quickly and become almost undetectable. This is true for many pregnancy-related hormones produced by the placenta. For example, hCG drops quickly, as does estrogen, and another hormone called hPL (human placental lactogen). The sudden drop of all these hormones at the same time is the trigger for the body to start breast milk production (lactation). Interestingly, there is no method that we know of to administer hormones to a woman who isn’t pregnant in order to duplicate the breast changes involved in lactation and allow her to lactate.

During breastfeeding, nearly all female hormone levels remain low. This is due (in part) to the effects of prolactin (the lactation hormone). High prolactin levels caused by nursing work on the ovary to keep it dormant, so during breastfeeding women normally do not ovulate or menstruate. This is called lactational amenorrhea, and while the pregnancy rate for breastfeeding women is low, this is not reliable enough to completely depend on lactational amenorrhea for birth control.

hCG Levels in Early Pregnancy

The abbreviation hCG is short for “human chorionic gonadotropin” hormone. This is the hormone that pregnancy tests look for, typically a week or two after conception, when your body begins producing various hormones to ensure that your developing baby receives all the nutrients and oxygen it needs. The hCG hormone is made by the cells that form the placenta. The detection of hCG in urine via a home pregnancy test may be the first indication that you are pregnant. Since hCG is only made by placental cells, it is not normally found in the body, thus the detection of even a very small amount of hCG in the body indicates that placental cells are present.

There are two types of hCG tests: qualitative hCG tests, which detect the presence of the hormone in urine or blood, and quantitative hCG tests, which measure the amount of hCG present in the blood. Quantitative hCG tests are also known as beta hCG tests (doctors have nicknamed the test a “quant beta”). The hCG hormone can typically be detected in the urine eight to fourteen days after conception, and in the blood as early as six days after implantation—before the first missed menstrual period. Measuring hCG levels is the best way for healthcare professionals to detect early abnormalities after the pregnancy has been established. In 85 percent of pregnancies, hCG levels double every 72 hours before peaking between the eighth and eleventh weeks of pregnancy. After peaking, the levels begin to decline between the twelfth and sixteenth weeks of pregnancy, and then level off until after childbirth.

What do hCG Levels Mean?

The hCG hormone is produced throughout your pregnancy. Initially hCG maintains the corpus luteum, which is responsible for progesterone production during the early stages of pregnancy. Progesterone’s major job is to maintain the thickness of the uterine lining. A thick lining increases the chances of a healthy pregnancy. If there is no hCG present in your body, the lining will begin to shed and you will begin your period shortly after. Basically, in a normal menstrual cycle, the corpus luteum is created right after ovulation, and it has a lifespan of 12–13 days (producing progesterone). When pregnancy does not occur, the corpus luteum disappears, progesterone production stops, and the menstrual period occurs after a day or two.

The most important thing to remember when examining hCG levels is that every pregnancy is different, and every woman is different. What is normal for one woman is not necessarily normal for another woman. Some women have low hCG levels throughout their pregnancies and have healthy babies. Some have extremely high hCG levels in early pregnancy and can still go on to miscarry.

The hCG hormone is measured in milli-international units per milliliter, or mIU/ml. Typically, when you are not pregnant, your levels are less than 5 mIU/ml. When you are pregnant, your hCG levels will be 25 mIU/ml or higher. If levels are higher than expected based on how far along you are, it may indicate twins or multiple fetuses, a molar pregnancy, or a miscalculation of the pregnancy date. Unexpectedly low hCG levels may also indicate a miscalculation of the pregnancy date, or possibly a miscarriage, an ectopic pregnancy, or a blighted ovum (another type of miscarriage). Often one measurement is not enough. Second or third measurements, especially taken days apart, can yield more accurate results.

Fertility drugs that contain hCG may affect your hCG levels. You and your healthcare provider should discuss this topic if you are currently taking fertility drugs. Other medications such as antibiotics or oral contraceptives do not affect your hCG levels.

If you decide to use a home pregnancy test before seeing your doctor, be aware that all home pregnancy tests detect only the presence of hCG in urine, and the level of hCG each test can detect varies. While urine tests are convenient and relatively inexpensive, they are not as accurate as quantitative blood tests, and can produce false positive results.

hCG and Birth Defects

Depending on your fertility history, age, past pregnancies, and other factors, your doctor may want to track the rise in hCG over a few days or weeks. This means going in for a second, third, or fourth blood test. In a healthy pregnancy, the results should double every 48 to 72 hours. An hCG level that does not rise as expected may indicate a problem with the pregnancy, such as a miscarriage or an ectopic pregnancy.

Pregnancy testing is not the only reason to test hCG levels. They are also used to detect fetal abnormalities that may result in birth defects. During a prenatal visit, your doctor may want to give you a Quadruple Screen Blood test. This test measures the alpha fetoprotein levels, as well as the levels of hCG, estriol (a form of estrogen) and inhibin-A to help evaluate the risk that your baby might have Down syndrome or a spinal or brain abnormality. hCG can also help determine whether a miscarriage has occurred or is going to occur.

hCG Levels and Gender

In a human reproduction study conducted by a team of Israeli researchers led by Dr. Yuval Yaron, 1,325 pregnant women were tested at 10–13 weeks to compare hCG levels between women carrying female fetuses and women carrying male fetuses. The findings were conclusive: women who had a female fetus had significantly higher hCG levels than women carrying males.

The authors noted that the reason for the gender-related difference in maternal serum hCG has remained elusive since the phenomenon was first described in 1965. Based on these studies, some have speculated that it may be possible for woman carrying a male fetus to have a delayed positive urine pregnancy test result because of the lower level of hCG. However, Dr. Yaron and his colleagues concluded that while the gender-related difference in maternal hCG levels is statistically significant, it has little value in predicting fetal sex because of the small proportion of pregnant women with serum HCG concentrations that are high or low enough to allow a prediction with high probability.

In other words, there is no way to definitively know the gender of the baby you’re carrying without undergoing one of the following:

  • Amniocentesis or chorionic villus sampling, both of which are invasive and costly.
  • A blood test to detect Y chromosome-specific DNA (the presence of Y chromosome DNA confirms a male fetus). This noninvasive test can be done at 10 to 12 weeks’ gestation and may or may not be covered by insurance but may be less costly than invasive methods. It is part of a panel called NIPT (non-invasive prenatal testing).
  • Ultrasound evaluation: evidence of fetal sexual organs can sometimes be detected as early as the 12th week of pregnancy, although more often not until 16 weeks.

Although it might be fun to speculate about the gender of your baby if your doctor tells you your hCG level after quantitative blood testing early in pregnancy, it would wise to wait until after definitive test results before picking out baby clothes and colors for the nursery.

Additional facts about hCG levels:

  • Later in pregnancy, hCG levels mean little to how well the pregnancy is doing.
  • hCG levels should not be used to date pregnancies, since the numbers vary so widely from woman to woman
  • Single hCG tests are typically not enough for an accurate diagnosis.
  • A transvaginal ultrasound should be able to show a gestational sac inside the uterine cavity if the hCG levels have reached 1,000 to 2,000 mIU/ml. Ultrasound findings lower than 2,000 mIU/ml should not be used to determine the date of conception because levels can vary greatly. For example, hCG levels are much higher for twins, so a very high level of hCG without the presence of a gestational sac might also mean a twin pregnancy.
  • Urine hCG levels are typically lower than blood levels.

[Page updated June 2016]